Mold wash composition



y 23, 1968 P. J. NEFF MOLD WASH COMPOSITION Filed Jan. 19, 1966 v mm. xw w ww Q g a? f 5: Z 5 J 1 0. W E w Ma P Mr 55s United States Patent 3,385,717 I MOLD WASH COMPOSITION Paul J. Naif, Lansing, Ill., assignor to Armsted Industries Incorporated, Chicago, 11]., a corporation of New Jersey Fiied Jan. 19, 1966, Ser. No. 521,656 6 Claims. (Cl. 10638.23)

The present invention relates to a mold wash for shell molds and to a method of casting.

A broad object of the invention is to provide a novel mold wash and method of casting whereby to minimize and eliminate certain defects in castings formed in shell molds, such as described in United States Letters Patent No. 3,121,269.

A more specific object is to provide a mold wash of the character just referred to which reacts with the metal of the casting to control the molten condition thereof during the casting operation and thereby prevent the formation of positive defects on the casting outwardly beyond the originally intended shape of the casting.

A still more specific object of the invention is to provide a mold wash for shell molds in the use of which oxygen is liberated therefrom and combines with the hydrocarbons and carbon monoxide of the mold to prevent carburization of the casting and thereby prevent the formation of positive defects on the casting.

Other objects and advantages of the invention will appear from the following detail description taken in conjunction with the accompanying drawings in which- FIGURE 1 is a semi-diagrammatic view of one part of a mold, showing a casting therein;

FIGURE 2 is a fragmentary view of a portion of the casting represented in FIGURE 1, showing positive defects of the kind the present invention is particularly adapted to eliminate; and

FIGURE 3 is a cross-sectional view through the casting of FIGURE 2 taken at line 33 of the latter figure.

The present invention is concerned with defects that are formed on castings due to certain conditions that exist within the shell mold as well as possibly other conditions referred to hereinbelow. The invention is specially adapted to minimizing and even eliminating such defects. In casting operations the condition of the atmosphere in the mold is of course of very great importance in producing a proper casting, and more specifically producing a castm-g having a good surface. If the atmosphere is reducing, the surface of the casting will tend to be carburized. If the atmosphere is oxidizing, the surface of the casting will tend to be decarburized. In this invention, the mold atmosphere consists of not only the gases given off by decomposition of the organic binder but gases given off by decomposition of the wash that is usually applied to the surface of the mold cavity.

In many instances a casting, due to volumetric size, shape, mass, and possibly other physical characteristics, assumes distortions in the casting operation so that portions of the casting are separated from the surface of the cavity, leaving spaces therebetween in which atmosphere develops that is detrimental to the casting, for example, forming objectionable surface thereon.

An example of such a casting is represented at It) in FIGURE 1, which is a brake beam. The mold utilized may be a shell mold of known kind, in the formation of which a model is placed on a surface and covered with sand which is then cured to form a mold part utilized with a counter mold part together forming a cavity into which molten metal is poured. The cavity thus formed is shown at 12 in the mold part 14 which is positioned with its mating face exposed. The brake beam, because of its physical characteristics which are selected vfor its function in a railway car, experiences action which causes conditions that are deleterious to the casting. More specifically, the

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brake beam is of elongated shape having end elements 16 and-a bottom tension member 18. When the molten metal is poured into the cavity, it begins to freeze immediately, and the outer surface portion of the casting forms a relatively solid shell enclosing a central portion of metal that is still more molten. The pouring step is completed rapidly, requiring only a fraction of a minute, and in another short interval of time, such as in a minute or less, the outer shell on the casting referred to is formed. This shell has suflicient strength to support the casting, at least to a degree. In the present instance the lower portion 20 of the tension member 18 of the brake beam separates from the corresponding surface 22 of the cavity and rises to a position represented by the dot-dash line 24 leaving a space 26 between the surface of the casting and the surface 22 of the cavity. The brake beam is supported by the end elements 16, the latter being at that time of sufficient strength to support the casting to the degree necessary, with the result mentioned, that the bottom portion of the casting separates from the corresponding surface of the cavity.

The invention has applicability to conditions of the kind just described, regardless of the kind of casting made, i.e., regardless whether it is a brake beam or any other device, the invention is applicable to any kind of casting where any portion thereof separates from the surface of the cavity during the casting operation. Additionally, this action need not take place at the bottom of the casting, although it may occur at that location more than at any other location. The kind of casting shown and described above is selected merely as an example of the conditions and circumstances existing and to which the present invention is particularly adaptable.

When the casting so separates from the surface of the cavity, heretofore the atmosphere in the space 26 carburized the surf-ace of the casting and lowered the melting point thereof. In the case of a massive casting, the solidified outer shell thus formed is relatively thin and a substantial mass of metal in the interior that is still molten remains. The lowering of the melting point of the casting, which takes effect principally at the surface, re-melts the surface, due to the specific heat in the molten center, and as a result the metal that constitutes the former solid shell, and which is now again molten, begins to run and forms positive defects indicated at 28 in FIGURES 2 and 3. The casting represented in these figures has a bottom main surface 30, constituting the desired final shape of the casting according to its original design. This surface corresponds to the dot-dash line 24 of FIGURE 1, which at the time referred to is spaced from the bottom surface 22 of the cavity. The positive defects 28 may assume any of various forms as drapes, spikes, jagged edges, etc., and they must be removed from the casting when they exist which, as has been heretofore performed such as by grinding them oil, is time consuming and expensive, The present invention eliminates the formation of these positive defects.

The present invention involves the application of a mold wash to surface of the cavity in the form of a continuous film, before the casting operation. This mold wash includes oxygen which is liberated and combines with the carbon of the casting and prevents the carburiza-tion thereof. The form of the mold wash is an iron oxide, Fe O This iron oxide (Fe O is a relatively unstable oxide and upon its reaching an elevated temperature, one atom of oxygen is easily liberated. It is believed that this liberated oxygen combines with the carbon in the metal of the casting and prevents the carburization referred to above. It is further believed that the remaining material of the mold wash, which is in the form of =FeO, remains stable and maintains its integrity as a covering film on the surface of the cavity. Iron oxides other than Fe O have not proved satisfactory. The mold wash is preferably made up of the following ingredients:

Percent 7.0 lb. Fe O 47.6 0.5 lb. dextrin 3.4 0.5 gal. water 27.2 0.5 gal. alcohol 21.8

This wash may be prepared by first mixing the water and alcohol, and mixing the iron oxide and dextrin together in a separate container. This latter mixture of iron oxide and dextrin is then slowly added to the first mixture of water and alcohol and during this step the ensuing total mixture, which is in the form of a slurry, is mechanically agitated to provide complete dispersion of the solid particles. If desired, the wash may be agitated by bubbling air therethrough.

The foregoing mixture requires very little agitation to maintain the solid particles in suspension. It may be mechanically or manually agitated only moments before it is to be applied to the surface of the cavity, and is so applied by any suitable means such as by a conventional spray gun. The wash is most easily and most effectively applied by spray when it has a viscosity in the range of about 45 to 50 Baum. If the viscosity should fall below that range the total amount of oxide applied may not be sufiicient, while if the viscosity is above that range it may be difficult to spray but may still be applied by brushing onto the mold in which case the Baum range may be about 3080. However this range of viscosity has principal importance from the standpoint of application of the wash to the mold, rather than the effectiveness of the wash after it is applied, in preventing the defects referred to.

The iron oxide may be effectively applied to the mold when it is present in the wash in the range of about 30% to 60% by total weight. The dextrin acts as a binder and may be present in the range of about 2% to about 8% by total weight. Obviously other binders may be used such as, for example, starch or water dispersible phenolic resin.

The water and alcohol are preferably present in approximately equal amounts, although either of them could be used alone to form the slurry. However, if only water is used, the slurry dries much more slowly and does not penetrate or adhere to the mold as readily as when made with water plus alcohol. On the other hand, if only alcohol is used, the cost of the slurry increases and, further, the solids tend to settle out too rapidly. The water and alcohol should each be present in the range of about to 45% by weight of the wash, with the combination being present in the range of about 30% to 60% by total weight of the wash.

Preferably the iron oxide is of a character known as pigment grade, the great bulk of which is of very fine particles as small as in the neighborhood of one micron. Larger particles may of course be used, but the smaller sized particles provide a distinct advantage, the particles are more easily maintained in suspension, and the wash is more easily sprayed on the mold. Preferably a product put out by Foundries Materials Company of Coldwater, Mich., and known as #604 Black Iron Oxide is utilized in the mold wash. This material is constituted by particles of which substantially 99% of the particles will pass through a 325 mesh screen, the average particle size is substantially 0.5 to 0.7 micron and 95% of the particles are less than 1 micron. Notwithstanding the foregoing desired particle size, the wash is elfective in utilizing materials in which the particles range to as high as in the neighborhood of 74 microns. The advantage of small particle size resides more in the ease with which the Wash can be applied rather than in the effectiveness of the wash after it is applied.

The wash thus formed is applied to a thickness of up to .010 inch while thicknesses of in the neighborhood of .004 to .006 inch have produced good results. Of course various thicknesses may be utilized in different applications. Generally speaking, and other factors being equal, the greater the massiveness of the portion of the casting concerned, the greater should be the thickness of the mold wash, to provide the desired oxygen from the mold wash to combine with the carbon of the metal of the casting.

The mold wash is normally applied to the shell mold casting surface while the latter is at quite an elevated temperature. As a consequence, the water and alcohol rapidly evaporate and in the normal routine of forming castings the water and alcohol are evaporated well before the metal is poured. In the remaining portion of the wash, the dextrin is utilized to form a binder or glue to adhere the iron oxide to the mold and to maintain the film in continuous and unbroken form. The dextrin does not deter the action of the oxygen in the oxide in combining with the hydrocarbons and carbon monoxide in the mold atmosphere, thereby preventing carburization of the casting.

While I have disclosed herein a preferred form of the invention, it will be understood that changes may be made therein within the scope of the appended claims.

1 claim:

"1. A mold wash for shell molds, said wash containing iron oxide in the form Fe O 2. The mold wash set out in claim 1 wherein the mold wash includes a binder and liquid, forming a slurry capable of being sprayed, dipped or brushed.

'3. A mold wash according to claim 2 wherein the slurry is of a viscosity of in the range of about 30 to Baum.

4. The mold wash set out in claim 3 wherein the mold Wash includes about 30% to 60% by weight Fe O and about 2% to 8% by weight dextrin.

5. The mold wash set out in claim 4 which also includes about 5% to 45% by weight water and about 5% to 45% by weight alcohol.

6. A mold wash according to claim 5 in which the iron oxide is made up of particles substantially as follows: 99% thereof will pass through a 325 mesh screen, the average particle size is in the neighborhood of 0.5 to 0.7 micron and substantially of the particles are less than 1.0 micron.

References Cited UNITED STATES PATENTS 2,641,525 6/1953 Walter et al. 106-3823 X 3,042,541 7/ l962 Kaplan 1l7-5.3 X 3,193,888 7/1965 Rochester 117-5.3 X 3,326,273 6/1967 Iago 106-3827 X J. SPENCER OVERHOLSER, Primary Examiner. E. MAR, Assistant Examiner. 

1. A MOLD WASH FOR SHELL MOLDS, SAID WASH CONTAINING IRON OXIDE IN THE FORM FE3O4. 